Transistor phase detector



Jan. 14, 1958 5. o. D'NEi` Y ETAL TRANSISTOR PHASEy DETECTOR f N A w f MW. m um WM W U Mw w .c 0 D e c E f 4 -IL 9 4 n I nnd d. d. q w y 1 M ,Y ||||ll k W 7 AAM 0F] M MM a N 4. 6 .YwN Y@ miv? miv* 2) 6 LN @"mx Nm Aly .Eifer-.5.

TRANSISTOR PHASE DETECTOR Gregg 0. DNelly, Santa Monica, and Norman B. Fieldsted, Los Angeles, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application April 19, 1955, Serial No. 502,319

6 Claims. (Cl. 250-31) This invention relates generally to discriminator circuits and, more particularly, to circuits for comparing the phase of a reference signal with respect to the time of occurrence of a comparison signal.

Circuits which compare two signals, detecting differences therebetween, and produce an output D. C. voltage which is indicative of the relationship between the compared signals are well known to the art. Such a circuit is commonly referred to as a phase detector or a phase discriminator. Detailed discussion of the various types of phase detectors and their possible applications may be found in chapter 14 of volume 19, Radiation Laboratory Series, entitled Waveforms, published by McGraw-Hill Book Company, Inc., New York, 1949.

The circuits of this type which are currently used ernploy vacuum tubes as their active circuit elements. Because of the use of vacuum tubes, it is necessary to have power supplies, biasing supplies, and heater voltage supplies for proper operation. Many circuits of this type require a capacitor and resistor connected in parallel and placed in the grid circuit of the tube or tubes to keep the tubes from conducting during the period when no signals are applied thereto. Even though a vacuum tube when not conducting has substantially inlinite resistance when conducting it represents some finite resistance which may be of the order of 100 ohms or more, depending upon the grid voltage, thus placing a further limitation on these phase detectors.

Accordingly, it is an object of the present invention to provide a phase detector which has substantially iniinite impedance when in a non-conducting state, and substantially zero impedance when in a conducting state.

Another object of the present invention is to provide a phase detector having substantially fewer circuit components than presently used phase detectors, thus resulting in lower manufacturing costs, smaller size, and less maintenance, and having an overall increase in reliability.

A further object of the present invention is to provide a transistor phase detector which operates with no directcurrent bias or power supplies and which producesta direct-current voltage level outputfsignal which is representative of the phase relationship between two signals to be compared.

A phase detector in accordance with the present invention comprises two interconnected transistors, each having an input, an output, and a common electrode in contact with the transistor body. A comparison signal is applied simultaneously across the input and common electrodes of each of the transistors through appropriate coupling circuits. This causes each of the transistors to change from its quiescent non-conduting state to a possible @on1 duc'tive state. A reference signal is simultaneously applied through other coupling circuits across the output and common electrodes of each of the transistors. If the two signals are applied concurrently to the transistors, one or the other of the transistors will conduct, depending upon thephase relationship between the signals. -The latent() 232mm VVPatented Jan. 14, 1958 vverted to a direct-current voltage level in a charge storage device which is connected across the output and common electrodes of each of the transistors. The amplitude and polarity of the direct-current voltage level is representative of the phase relationship between the applied reference and comparison signals.

The novel features of the present invention are set forth in particularity in the appended claims. Other and 'more speciiic objects of the invention will become apparent from a consideration of the following description .taken in. connection with the accompanying drawing in which:

Fig. 1 is a circuit diagram, partly in block form, of the preferred embodiment of the phase detector of the present invention;

Fig. 2 is a graph illustrating waveforms takenvat various points in the circuit of Fig. l; and

Fig. 3 is a graph illustrating the collector voltage-current characteristics of a junction transistor with a load of the type used in the circuit of Fig. l.

Referringnow to the drawing and, more particularly, to Fig. 1, there is shown a transistor phase detector circuit including two transistors 11 and 12, each represented by their accepted schematic symbol. The semiconducting body of transistor 11 has an input or emitter electrode 13, an output or collector electrode 14, and a common or base electrode 15 in contact therewith. The semiconducting body of transistor 12 has an input or emitter electrode 16, an output or collector electrode 17, and a commonor base electrode 18 in contact therewith. Transistors 11 and k12 may be junction transistors of the N-P-N type. A transformer 21, having a primary winding 22, a iirst secondarywinding 23, and a second secondary winding 24, is employed as a coupling device in the transistor phase detector of Fig. 1.

Comparison signal source 25, which has one terminal 26 that is grounded, is connected to one side of primary in a polarity such that the transistor is in a condition to conduct as shown by negative pulses 38 and 39. Diode 27 is connected between collector 14 and base 18. Diode 28 is connected between collector 17 and base 15. Each ofthe diodes 27 and 28 is poled topass only current flowing through collectors 14 and 17 into the semiconducting body of transistors 11 and 12, respectively. Coupling capacitor 31 is connected between base 18 and reference signal source 32 which has a second terminal 33 that is grounded. Dropping resistor 34 is connected between base 18 and ground. A charge storage device, such as capacitor 35, is connected between base 15 and ground. Also connected across charge storage capacitor 35 are output terminals 36, one of which is grounded.

In discussing the operation of the circuit of Fig. 1, reference will be made to Fig. 2 wherein the abscissa represents time and the ordinate, voltage. During normal operation, a continuous, periodically recurring reference signal, such as the sine wave 41 of Fig. 2, is applied through coupling capacitor 31 to base 18 and through diode 27 to collector 14 of transistors 12 and 11, respectively.

current ilowing through the selected transistor is con'-` Since no bias is applied to emitter electrodes 13 and 16 of the transistors, each of the transistors is electively cut off. Therefore, the reference signal will not be passed `by either ofthe transistors.

Assuming now that a comparison signal, such as pulse by either transistor 11 `or .12,'appearingas a charge upon capacitor 35. :During .the time that reference signal 41 is negative with respect to itszeropoint and ,puls e.42

is applied tothe transistors, collector 17'is positivewith respect'to base 18. Therefore, transistor'12 willconduct,

tending to charge capacitor `35 negative with respect,v to

jground. Transistor 11 cannotconduct during this time 'since the negative portion of reference signal A414 is blocked (by diode `27. After reference signal 4Lpasses through'its YzeropojntA and vbecomes positive,transistorf11.will rconduct 'provided comparison signal 42 `is still applied thereto.

This occurs because thepositive reference .signaldl is passedby diode 27, causing collector .-1.4.tobe`come positive with respect to base 15. .This conduction tends to charge capacitor v35 positive. with respect Vto ,.gronnd. Transistor '12 cannot conduct. during Vthis vtime .because collector V17 is negativewithrespectltobase.18. .Since "the charge appearing across, capacitor 3A51during the/.time

.each transistoris conducting isoppositefin ,po1arit-y,the net chargeupon capacitor,35.ris .zero, as indicated; bythe @heavy Vportion .213 of the directfcurrent `output voltage curve of Fig.`2. tlf at oneperiod or cycle laterreferring to lthe .reference signal, another ,comparison nl.signal pulse, such .as .42', .occurs as Athe ,reference signal is passing ,throughV zerothe. direct-current output voltage oo capalcitorf35 will remain-.at rzero,asvs hown.

If at some later time, such .as t1, onFig. Zfanotherpulse, ,such as .44. t is applied t` transistors .-11 fand 1-2ffr0m-l0mr parison signall source .25,and reference v signal 41 is1posi- .tive vdurin-gthe duration ofthe comparison signal, fas shown in Fig. 2, transistor 11 will. conduct, charging capacitor 35L positive with respectto iground,a,sshown. by output signalv 45 of the direct-current output voltagecurve .in Fig. `2. Transistor 1-2 will -not condnctsince the:posi- .tive signal applied directly to base 18 .is eiectivelyamegative signal on collector 17. Afterthe occurrence 'ofgpulse 44, the `charge on Hcapacitor 35 will tend to leak olf. Since noeomparisonsignal is appliedat `this'time, transistors 11 and .12 are cutfol, and they `represent 'a\sub vstantially infinite impedance .to the discharge path. of capacitor 35. Thedischarge ot'zthefcapacitor will, there fore, be extremelyeslow. .If anotheracomparison signal pulse, such as 44", is vthenapplied to .transistors 11..and 12 and .it has `the same phase .relationship with .reference Asignal41 as didpulse 44, capacitori35 `wi-llagainfh'echarge'd to the maximumvalue. of reference. signal llwhichioccurs 'duringthe period that:.the comparison-pulse .isl'applie'd to theztransistors.

`Assuming now that at .some slater Stime, 'such as retira, -a 'comparisonsignaL such as. pulse 147,:.is applied fto transistors 11 and 12 while referencesignal =41 -is negative. Since .diode27 .willaallow only a positive goingv signal Ato be applied .'totransistor 11,- transistor 11 will remain I cut oiduring thisperiod. However, the negative reference signal is applied directlyto base 18 of; transistor 12. This is equivalent to a positivesignal applied/to-collector A1-7. Therefore, transistor 12 will jconduct, allowing current tofow toward the v semiconductor body Aof transistor L12, thus charging `capacitor 35 negative'with respect -`tov ground, as 'shown .by -48 on the direct-current-outpnt -volta'ge ycurve of -Fig.,2. As before, the charge 'jappearingon 'capacitor i35 will-tendtoslowly` leak ofi". ^However,' 'asia subsequent pulse from theVv comparison lsignal source, such as 47...is applied ,to transistorsdjlfand ,1.4,. tria-lnister.1.(2 I willagain conducerestoring .theharsepnecanaslor sistors, as shown by the schematic symbol in Fig. 1.

-I-so,^ the voltage-current characteristics lookingv intoY the collector electrode of either of the transistors will be as shown in Fig. 3, wherein the abscissa represents collector current Ic and the ordinate, collector voltage Vc. If the period of duration of the comparison signal which is applied to the transistorsis very short compared to the period of fthereferencefgsignal, the'voltage appearing on thecollectors ofv each of the transistors can be considered as substantially; constant. f lf 1no; comparison signal: isv applied to transformer '21, 'theem'itter current will `befnero andthe collector'voltgeicnrrent curve will be, asishown in Fig. 3, for this condition, IE=0. Although some collectorcrrent-niyow? under these=conditions,no-`charge will appear on ,capacitor T3:5 sinceboth transistors will conduct equally"bt in "opposite'directions during respective half cycles ofthe reference signal. Assume that when acomparison s ignalisnapplied to the transistorsthe-reference signal voltagehajsfa "certain value, a's shown `at- 6.1 o'n Fig. 3. "This establishes the operating point ofthat transistor whichwould conduct. at point 61 on Figj3. Atthispoint,collectorfcurrent is very low and collector voltageY isiq'uitehigh; therefore, the resistancerlookinginto lthe'collectoris' large, on'the lorder of megohms. As' time progresses, "emitter current'begins rtov ow, and collector currentinicreases. However, sincethe loadin the collector circuit'f'the ftr'ainsi'stor is'a capacitor, vthe voltageappear- Ving aerosfs the ."collecto'rlha'se of the transistor Ycannot change 'instantaneoufSl-yand will, therefore, remain as a sornefnite-periodof time, as shown by 'curve '6`2^ oF 1`g. l3'. Y

yAs. capacitfor,35 charges, fthe voltage appearing across the. collector-basent ,theftransis'tor willy begin to decrease,

`asShow/n.531Qthe,curved portion.63 of line 62 in Fig. 3.

collector current iis :.at its maximum and the.. collector voltagefis-iat'itsfrninimum,` therefore'causing rthe resistance looking intothefcoHect'orof. the transistor to be verylow, ontherorder '015:30 tof4`0 .'ohms.

Iticantibe seen,1therefore,.thatlinel62, in Fig. 3,r`epre seats-.the `load linenwhich-is seen V.bythe transistor dueto capacitor .35,.fand'that when :no comparison signal is appliedl to theft'ransistors, the limpedance looking into the collectorlis "extremely Jhigh, and when a 'comparison signalisfappliedftollthe transistors, the impedance lookingfi'nto the collectoris Vsubstantialy zero. Therefore, transistors -v11#a`n`d -152 `operate lsubstantially like a switch, being open during `the time when no comparison signal is applied, fandclosed when one is applied. During the time theswitch is closed, the'comparison signal isrpassed by ione orthe other of lthe transistors, thus charging capacitor 35po'sitiveor negative with respect to ground, depending lupon'the polarity o'fthe reference signal at this time.

-t' is to be understood that. whilea phase 'detector 'ernployin'g'onlytwo;transistorsfand comparing the two signals once'eachperiofdis shown in Fig. l and describedlin'this application, 'one ski'lljedjin-the -art can readily 'js'eeihat -an extension @hereto 'fmay "be made by "employingjtwo output iclapaciforsj'tog'ether 'at ja common pointandground- Athis point. NResistori314 may :thenbegominedifrnnt each of the circuits as well. A detector which will compare the reference signal with the comparison signal every 180 of the reference signal can be thus obtained. It can be further seen that by varying the occurrence of the comparison signal so that it repeats every 90 of the reference signal, an orthogonal phase detector may be obtained.

It should also be noted that transistors other than of the N-P-N junction type may be utilized in this circuit. For example, if P-N-P junction transistors were to be used, all that would be necessary is to reverse the polarity of diodes 27 and 28 and reverse the polarity of the applied comparison signal in order to obtain the same results. As another example, one transistor may be of the P-N-P type and the other of the N-P-N type. By properly connecting the diodes 27 and 28 and the transformer 21, the operation and results above described may be obtained.

It should be understood that, the circuit specifications for the transistor phase detector shown in Fig. 1 may vary according to the design for any particular application. The following circuit specifications are included by way of example only, and are suitable for operation with reference and comparison signals having a frequency of from zero to 1,000 cycles per second.

Transistor ll-N-P-N junction transistor, Germanium products 2501.

Transistor 12-N-P-N junction transistor, Germanium.

products 2501.

Transformer 21-Pulse transformer capable of passing 250-microsecond pulse.

Diode 27-Silicon junction diode, Texas instrument T-lO.

Diode ZHilicon junction diode, Texas instrument Capacitor 31-1 microfarad.

Capacitor 35-10 microfarads.

Resistor 34-100 ohms.

There has been thus disclosed a preferred embodiment of a transistor phase detector for producing a directcurrent output voltage level which is representative of the phase relationship between an applied reference signal and an applied comparison signal which has a substantially infinite impedance when the transistors are nonconducting, and substantially zero impedance when they are conducting. Furthermore, it should be noted that no direct-current bias supplies or power supplies are used at any point of the transistor phase detector circuit of the invention.

What is claimed is:

1. A transistor phase detector for producing directcurrent voltage levels in response to the phase relationships between applied reference and comparison signals comprising: a first transistor, including a first emitter electrode, a first collector electrode, and a first base electrode; a second transistor, including a second emitter electrode, a second collector electrode, and a second base electrode; first coupling means connected between said first emitter and base electrodes and said second emitter and base electrodes for applying the comparison signal to each of said transistors simultaneously in a polarity to cause each of said transistors to be conditioned to conduct; a first unidirectional current flow device connected between said first collector electrode and said second base electrode; a second unidirectional current flow device connected between said first base electrode and said second collector electrode; second coupling means connected between said second base electrode and a common terminal point for applying a continuous periodically recurring reference signal to each of said transistors simultaneously to cause either said first or Asaid second transistor to pass the comparison signal during the time the reference signal is applied concurrently therewith; and charge storage means connected between said trst base electrode and said common terminal for` converting said comparison signal to a direct-current' having a primary winding, a first secondary winding, and' a second secondary winding, said tirst secondary winding being connected between said tirst emitter and base electrodes, said second secondary winding being connected between said second emitter and base electrode, said primary winding being connected between a comparison signal source and a common terminal for applying the comparison signal to each ot' said transistors simultaneously in a polarity to cause each of said transistors to be conditioned to conduct; a first unidirectional current tlow device connected between said first collector electrode and said second base electrode; a second unidirectional current liow device connected between said first base electrode and said second collector electrode; second coupling means connected between said second base electrode and a common terminal point tor applying a continuous periodically recurring reference signal to each of said transistors simultaneously to cause either said first or said second transistor to pass the comparison signal during the time the reference signal is applied concurrently therewith; and charge storage means connected between said first base electrode and said common terminal for converting said comparison signal to a direct-current voltage level, whereby a direct-current voltage level will be produced at said storage means representative of the phase relationship between the comparison and reference signals.

3. A transistor phase detector for producing direct-current voltage levels in response to the phase relationships between applied reference and comparison signals comprising: a. first junction transistor, including a first emitter electrode, a first collector electrode, and a first base electrode; a second junction transistor, including a second emitter electrode, a second collector electrode, and a second base electrode; lirst coupling means connected between said first emitter and base electrodes and said second emitter and base electrodes for applying a comparison signal to each of said transistors simultaneously in a polarity to cause each of said transistors to be conditioned to conduct; first rectifying means connected between said first collector electrode and said second base electrode; second rectifying means connected between said second collector electrode and said first base electrode; second coupling means including a capacitor connected between said second base electrode and a comparison signal source, an impedance element connected between said second base electrode and a common terminal point for applying a comparison signal to each of said transistors simultaneously to cause either said first or said second transistor to pass the comparison signal during the time the reference signal isapplied concurrently therewith: and charge storage means connected between said first base electrode and said common terminal for converting said comparison signal to a direct-current voltage level, whereby said first transistor will pass the comparison signal if the phase relationship between the comparison signal and the reference signal is of one sense and said second transistor will pass the comparison signal if said phase aseos-14s:

7 revationshipriszothe oppositefsense; and wherebyl-'saidt ohargegstoragmrneans: will ,-convert, the passedtcomparison: signal; tos a..- direct-.current rvoltage; level representativeio said; ghasearelationshp.-

4; 'Ihet transistor, phasef. detector. off claimL 3. wherein. said tirstr-.andsaidi-second junctiontransistors `are. each of: thea N-R-N type-andl said first. and second. -rectifyingmeans are poled to pass current flowing towardsaid first` andsecondcollector,electrodes.

5, .Ai-transistor, phase, detectorr for. yproducing directcurrent vol-tage,levelswepresentative.,of. the phase relaticmslrips4 betweenfapprlied reference and. comparison. signals. comprising; al `rstjnnction4 transistor. of.' the Nf- P-Nf type,I including,- aofirst. emitterl electrode, .an rstcollector,,electrodei andaa-rst .baser electrode; ,.a` second juntionftrainsistor; of. the Ns-P-N ltypeineluding a` sec-v ond emitterA elee'trod`ea t secondA collector. electrode,y and assecond .base.e1ectrode;rst coupling,meansincluding a transformer having; a, primaryI winding, ,atrst .seconda-ry,` winding, fand.asecond.secor1dary windingyisaidffrst.' secondary, Winding-.being. connectedzbetween .said .first emitten and .'b'ase electrodes, saidlsccondifsecondary. winding being, .connectedi between. said.l second emitter. `and 1 base electfod, .saidprimary, winclingQbeinge connectedbetween azcorngarison signal source.. and. a. common. terminal. .for apnlyinggannegativea goings comparison sigrialacrosslhe emitter. and.l base., electrodesJ of eacl`1,. 0L.V said transisttors` simultaneously to causeeach .ofsaidiransistors to..be,con.. ditioned toacondncn ,af'rst r diode,connectedabetween said'V first collector` electrode rand.. sadf. second. baseelectrode; a.` second diode connected. Betweenasaid. l second. collectorY eletto'deand'saidst;Ease' electrode, ,eaehlof A.said diods beinggpold Lto pass. current wiing;towardtsaidfcollector.v

electrodes; Ysecond coupling. .'rneans. including ,a1.capacitor. oonnectedbetnfeen said second baseeleetrode and a refer ence signl'ts'ource, anir'npednce element .connected'fbe.. tweenrsaid fsecond'bse electrodeamd .said commonrtermi! naLppnt fon appli/ing 'a reference` signalto, canili.oflsaid` transistors simultaneously in a. polarity, to. causeeither said 'rst .or said..secondftransistorio.passftlecomparison sig-nalldringthe time liereference .signal .is applied'fconcurrently( tl'erew'tihiand' a caplaeitor connected betWeen saids't Base electrode aridsaid'cmmon termial'for' converting said comparison signal to a.direct-currcnt volt"- agealevel,:wherebyt saidzrst transistor will-passthecomparison sigualLilt the Hphase'relationship.between the. comparisomsig-nal andthe'.- referencevsignal `is -of one sense` andsaidsecondtransistor. will pass the-comparison signal ifsaid` nhaseirelatinship. of the -ol'ipositey sense, .andA

. second utpureletod andasecond. common electrode,-

'rst coul-.ningV means connctedb'etween" said` rstiiiput andicomr'non' electrodes' a'rrd said secondinptand'; corn4 mon electrodesforapplifingthecomparison'signal to'e'ach of said transistors simultaneously in a pbl'rity'tocaii'se" eaclofsaitransistorstoliewdnditiohedltoconduct, 'rst asymmetically conductive 'means"connectedbetween Vsa'id first'ontput'-'elctrode'andisaidsecond'lcommon electrode; second-1asym'martial-Hy'l condcti've means connected betweensaid second 1output*eletrodeand'said st'- common electrodes-means"connect'lbetween' saidsec'ondcommon electrodeeand af common"te`r'rni`n'al lpo'it for applying the referencesignal tosaid .transistors simultaneously to cause eitlir sid`rst or said s'econd`transistor totr'anslate the comparisontsignal during,the .time the reference signal4 isv applied concurrently therewith,l and'icharge ,storage means connected between... saidV first common electrode and said common" te'rrrnalipoint` for converting" said' comparison signal .to aidirect current`voltagelev'el, where by 'aA direct current voltage level 'will b vp'rodnced at 'said charge storage means` representative of the phaserelationsti'pttetweenthe 1'comp'ariso'rrand reference signals.'

References Cited in thevle-.of this .patent UNITED STA-PES5P6J-1351sTSA 'f 

